Non-pressure sensitive, hot melt adhesives have many applications in the paper industry, including bookbinding, bag ending, and case and carton sealing. A non-pressure sensitive, hot melt adhesive based on an ethylene/vinyl acetate type polymer typically contains 30-40% polymer, 30-40% tackifying resin, and 20-30% wax.
When paper containing hot melt adhesives is recycled, hot melt adhesives typical of the prior art tend to liquify during repulping and adhere to the pulp, resulting in what is known in the industry as "stickies". H. Dahmane, "Repulpable Hot Melt Adhesives" European Adhesives and Sealants, page 28 (December 1992); T. F. Kauffman, "Environmentally Conscious Hot-Melt Adhesives" Tappi J. 74:142-44 (1991). Removing these clumps of adhesive and pulp increases the cost of paper recycling and residual adhesive reduces the quality of the resulting pulp. Also, adhesive deposit formation can lead to sheet breaks during the paper making process, thus leading to machine downtime.
Efforts to overcome this problem have included adding or replacing EVA type polymers with hydrophilic polymers. H. Dahmane, "Repulpable Hot Melt Adhesives", European Adhesives and Sealants, page 28 (December 1992); T. F. Kauffmann, "Environmentally Conscious Hot-Melt Adhesives", Tappi J. 74:142-144 (1991); S. L. Scholl et al., U.S. Pat. No. 5,143,961; J. N. Coker, U. S. Pat. No. 4,131,581; F. Brady et al., U. S. Pat. No. 5,217,798; "Aqueous Alkali-Soluble Hot Melt Adhesives," H. Nozawa et al., Japan Kokai Tokyo Koho JP 04 04,279 [92 04,279]; "Water-dispersible, Hot-melt Polyester-based Adhesives and their Uses," F. Bozich, PCT International WO 92 00363; A. S. Sheldon et al., U.S. Pat. No. 4,572,967. However, replacing the EVA type polymer weakens and reduces the durability of the hot melt formulation. The present invention has overcome the limitations of the prior art and describes hot melt formulations containing EVA type polymers that retain both adhesion and repulpability.